A simple immunohistochemical method for perinatal mammalian ovaries revealed different kinetics of oocyte apoptosis caused by DNA damage and asynapsis.

Oocytes with meiotic defects are assumed to be eliminated by apoptosis in the perinatal period. However, oocyte apoptosis caused by meiotic defects has not been well analyzed, partly because of the great technical demands of tissue sectioning perinatal ovaries. In the present study, we applied a squash method for immunohistochemical analysis of perinatal mouse ovaries as a substitute for tissue sectioning. As a result, we could show different kinetics of apoptosis caused by DMC1- and SPO11-deficiencies, indicating that DNA damage-induced apoptosis precedes asynapsis-induced apoptosis in mouse oocytes. Double-mutant analysis revealed that only asynapsis-induced apoptosis was significantly dependent on HORMAD2. The present method is simple, easy, and able to analyze a sufficient number of oocytes to detect infrequent events in a single specimen, accelerating detailed immunohistochemical analyses of mammalian ovaries during the fetal and perinatal periods.